The invention relates to an engine speed indicator for a vehicle, particularly to show an engine speed at which the engine emits a minimal amount of an emission gas.
The emission of different emission gases from an engine varies principally with the engine speed but the emission quantity also varies with other factors such as the delivered engine power. In Otto cycle engines, emission gases such as carbon dioxide, water, carbon monoxide, uncombusted hydrocarbons and nitrogen oxides are created during the combustion. In diesel engines, also sulphur oxides and carbon particles are created in addition to the above mentioned emission gases. For environmental reasons, it is important that vehicles are driven such the emissions of such more or less unhealthy emission gases are reduced as far as possible. The emission quantity of different emission gases of a vehicle varies with the specific properties of the combustion engine but also with the properties of the exhaust gas filter system. Therefore, the emission quantities of the emission gases may vary considerably between different vehicles. For. this reason, it is difficult for a driver to drive a vehicle such that the emission of the emission gases is reduced substantially optimally.
U.S. Pat. Nos. 4,244,210, 4,523,457 and DE 19621896 show engine speed indicators in vehicles, which comprise different kinds of indicating means, intended to indicate an engine speed at which a minimal fuel consumption is obtained. A number of emission gases are created in a quantity, which is substantially proportional to the fuel consumption. For example, carbon dioxide is created in a quantity, which is substantially proportional to the fuel consumption. Most emission gases are created in a quantity, which is related to different operation conditions. For example, the creation of carbon monoxide and nitrogen oxides is promoted. when a local lack of oxygen is the case, the creation of hydrocarbons when a high temperature and an oxygen surplus are the case and the creation of visible smoke (carbon particles) of diesel engines when the engine power is high and when the oxygen surplus is insufficient The emissions of these emission gases may be minimal at engine speeds, which considerably differ from the engine speed where the fuel consumption is minimal.